Universal Bore Hole Orientation (UBHO) subs have been used to drill directional oil wells since the 1960s. In order to drill a conventional directional oil well, UBHO subs have been used to orient borehole directional electronics with the bend in the drill string, thereby providing a datum orientation from which to steer the bit and drill pipe. A UBHO sub typically includes a sub connected within the drill string, with a sleeve installed inside the sub. The sleeve provides a metal alignment key. The key and sleeve can be rotated inside the sub to align the key with a bend in the drill string below the UBHO sub, and just above the bit. Once properly oriented, the sleeve is locked in place using set screws inserted from the outside of the sub.
When used with a Positive Displacement Motor (PDM) having a slight bend in the outer housing, directional drillers are able to redirect the path of the oil well bore by simply allowing the PDM to rotate the bit, without rotating the drill pipe. This technique, called “sliding”, enables a change of course while drilling by reorienting the bend to a new known direction.
Starting in about 1985, oilfield service companies began using retrievable “MWD” (Measurement While Drilling) systems containing borehole sensor electronics and mud pulse transmitters to transmit downhole numerical data in “real time” to the earth's surface via mud pulse telemetry. By doing so, MWD systems could show the orientation of the bend in the drill string while drilling, therefore allowing oil companies to “steer” a well path by sliding. Starting in about 1986, UBHO subs were adapted for use with MWD systems as the generally preferred technique for orienting directionally sensitive electronics in the MWD system to a datum orientation based on the bend in the drill string/PDM.
In about 1992, retrievable MWD systems were introduced in which the mud pulse transmitter was placed at the bottom of retrievable MWD systems, thereby requiring that the UBHO sub would incorporate the mud pulse transmitter assembly. With the new adaptation, the UBHO sub also incorporated a transmitter orifice in which a hydraulic valve stem could be positioned to create the pressure waves necessary to transmit encoded data from the MWD system.
The present form of the UBHO/Pulser sub has been used without major changes since 1992. However, beginning in about 2008, oilfield service companies began to use the technique of “horizontal drilling” to improve production of certain oil and gas bearing formations. The nature of horizontal drilling, however, causes extended sections of the drill pipe to lay horizontally in the well bore, thereby creating torque and drag issues which effectively limit the horizontal distance that drilling rigs can legitimately reach.
In response, many service companies began to design drilling tools that can physically excite the drill pipe axially (along the length of the pipe) in order to release the torque and drag (friction) of the horizontally-disposed drill pipe against the borehole wall. By doing so, the excitation drilling tools actually make the pipe and drill bit move in a telescoping fashion to keep the drill pipe surface in a “dynamic state”, while in contact with the well bore. By constantly moving the drill pipe axially, frictional forces between the drill pipe and the formation wall are greatly reduced. The end result is that directional drillers are able to drill and slide faster and further, thereby reducing the number of days to drill the well.
A major drawback to generating axial movement of the drill pipe, however, is that the telescoping axial forces are hard on the MWD systems in the UBHO sub. MWD systems include downhole sensors, electronics and mechanical packaging that are sensitive to shock and vibration. Studies have shown that the introduction of axial excitation of the drill string actually damages MWD systems once certain G-force levels are reached.
In order to protect MWD systems from shock and vibration, many MWD manufacturers have begun to provide 3-axis shock sensors with the MWD system, to alert personnel when shock levels reach damaging levels. Although the shock data can be provided in real time, often times MWD system damage is suffered before drilling parameters can be altered. The end result is often to simply accept that MWD systems are likely to suffer expensive damages in directional drilling operations, and to write the associated repair/replacement costs off as an overall cost of the drilling process.
Some prior art solutions have tried to protect MWD systems from high shock drilling applications with mechanical dampening packaging in “shock subs” below the MWD systems. Shock subs have been in existence for decades, and are commonly used when drilling in high shock drilling conditions. The disadvantage of shock subs below the MWD system, however, is that because such subs can average 7 feet in length, their introduction has the effect of locating the MWD electronics and sensors further from the bit, thereby making it more difficult to steer during drilling operations.
Another option to stave off potential damage to MWD systems has been to provide a shock absorber between the mud pulse transmitter and the electronics section of the MWD system to protect the MWD electronics from axial shock. As with the shock sub option, the MWD shock absorber also moves the MWD sensors further from the bit. It also does not provide protection for the mud pulse transmitter and UBHO sleeve from axial shock.
A third option is disclosed in U.S. Pat. No. 8,640,795, inventor Jekielek. A disclosed apparatus includes a UBHO sub, sleeve, and transmitter orifice riding on top of a shock absorber. Again, although the design reduces axial shock to MWD systems, it combines a UBHO sub with a shock sub, and thereby moves MWD sensors further from the bit.
There is therefore a need for a unitary shock absorbing UBHO sub that will protect MWD systems from axial and lateral forces during drilling operations, while still maintaining operably low MWD distance from the bit. Additional mud filtering capability may be provided on board. Advantageously, a customized mud pulser assembly will also be provided, adapted for optimal use with the shock absorbing UBHO sub, thereby enabling telemetry between the MWD equipment on board the UBHO sub and the surface.